Automated immunoassays are integral to clinical biochemistry, endocrinology and immunology. They can measure very small concentrations of analytes quickly and with impressive analytical precision. Yet precision does not mean every reported result reflects the patient's true biological state.
Some assays are vulnerable to interference from substances in the specimen or interactions with assay reagents. An affected result may appear internally consistent and pass routine quality-control checks. Recognition often depends on someone noticing that the result does not fit the wider clinical picture.
At a glance: Immunoassay interference occurs when substances in a specimen distort the measurement or its interpretation. Biotin, heterophile antibodies and other interfering factors can produce misleading results, depending on assay design. Laboratories should investigate results that conflict with the clinical picture using appropriate repeat, alternative-method or interference studies.
What is immunoassay interference?
An immunoassay relies on interactions between antibodies, antigens and labelled detection components. Other substances can disrupt these interactions, producing falsely high or falsely low measurements. The direction and extent of the error depend on the particular assay design.
Interference is not restricted to one discipline. It may affect thyroid-function tests, other hormone assays, cardiac biomarkers, tumour markers, autoantibody testing and selected specialist investigations. Importantly, not every assay using an immunological principle is affected in the same way.
Two common assay formats illustrate why the details matter. In a sandwich immunoassay, signal is generally related to the amount of target captured. In a competitive immunoassay, the relationship between signal and concentration is often inverse. An interfering substance can therefore lead to different apparent effects depending on the method.
Biotin: an important example
Some immunoassays use the strong binding between biotin and streptavidin as part of the analytical process. High concentrations of circulating biotin, sometimes associated with supplements or particular treatments, can interfere with these assays.
The US Food and Drug Administration has warned that biotin can cause erroneous results in some laboratory tests, including falsely low troponin results in affected methods. This is a method-specific risk, not evidence that all troponin or immunoassay systems are vulnerable.
Laboratories should know which assays in their test menu use susceptible designs and maintain appropriate advice for clinicians. Asking about supplement use can be relevant when investigating an unexpected result. Decisions about repeat sampling or temporary changes to supplement use should follow assay-specific information and clinical advice rather than a universal waiting time.
Heterophile antibodies and other biological interference
Heterophile antibodies or human anti-animal antibodies can interact with assay antibodies, sometimes bridging components in a sandwich method or blocking expected reactions. These effects can produce misleading results even when the sample looks normal.
Other recognised problems include macro-analytes, such as macroprolactin, which may be detected by a method without corresponding to the expected biologically active fraction. Very high analyte concentrations may also cause the high-dose hook effect in susceptible immunometric assays, leading to unexpectedly low measurements.
These examples show why laboratories need access to scientific interpretation and investigation pathways, not simply an analyser troubleshooting checklist.
Recognise results that do not make sense
An unexplained change in a marker, inconsistency between related tests or conflict with the clinical presentation should prompt review. The laboratory may examine specimen details, medications, supplements, previous results and the particular analytical platform involved.
Investigation methods can include repeat analysis, serial dilution where technically appropriate, treatment with blocking reagents, precipitation methods for macro-analytes or testing on an alternative analytical platform. Each approach has limitations and should be chosen by professionals familiar with the assay.
An alternative platform is helpful only if its design differs sufficiently to address the suspected interference. Similarly, a linear dilution response does not rule out every problem. Some investigations require referral to a specialist laboratory or discussion with the manufacturer.
Build an interference response into the quality system
The laboratory should document how suspected interference is escalated, investigated and communicated. Staff need to know when not to release a questionable result without further review and how to contact the appropriate clinical team.
Recurring incidents can reveal a need to improve report comments, test request information, staff training or access to alternative analytical methods. Monitoring these events also helps the service understand where risk remains despite modern automation.
The wider lesson is that analytical quality is not only about instruments meeting specifications. It is also about recognising the limits of the measurement principle. Strong communication between laboratory scientists and clinicians is often the decisive safeguard.
Where Optymum SS fits: Optymum SS can support assay evaluation, technical evidence reviews, training materials and laboratory quality documentation. Investigation and interpretation of individual patient results remain the responsibility of the treating team and authorised laboratory professionals.
Related on this site: Clinical Immunology, Clinical Biochemistry or Clinical Chemistry.
Key takeaways
- Consider interference when results and clinical findings disagree.
- Biotin effects are assay-dependent, not universal.
- Document investigation and communication pathways for discrepant results.
Frequently asked questions
What is immunoassay interference?
It is a change to assay behaviour caused by specimen components or other factors that makes a reported result inaccurate or misleading.
Can biotin affect laboratory tests?
Yes. High biotin concentrations can affect assays that use biotin-streptavidin chemistry, but the direction and size of interference depend on the individual test design.
How should unexpected immunoassay results be investigated?
Review clinical context and collection details, speak with the requesting team and use an investigation plan that may include alternative methods, dilution or interference-blocking techniques where suitable.
